73 R75/5 and 77 R75/7 Engine Commonality

[Beemerick]

I came across a guy with a 73 75/5 engine (non-running) for sale ($100), and was thinking of picking it up for possible parts use on a recently acquired 77 R75/7. The 77 runs well (aside from the ticking from the right exhaust ), but its mileage and history is largely unknown to me. I know the valve train is different (believe its already been removed from the 73 engine), but is there any value in me picking this engine up?

The ad says "...Bottom end of a r75/5 motor. has jugs (one has a stuck piston) crank, cam, timing gears and other various nicknacks. Good for parts... "

Thanks for your help.

[Major Softie]

If it's a good price, it is certainly worth picking up. What parts don't cross-over, can be sold to pay for parts that do. Whether or not there is "value" for you in buying this engine is completely dependent on the price/condition.

[Garnet]

There where lots of changes in late 75 for the 76 model year.

The holes in the block where the spigots of the cylinders slide into was enlarged from 97mm to 99mm.
The alternator windings went up to 107mm from 105mm meaning the timming chain cover changed.
The starter went from a 8 tooth drive to a 9 tooth and the ring gear changed in number of teeth at the same time in 76.
The crank went from 10mm flyweel bolts to 11mm.
The pistons are the same. The heads will fit but are different castings.
The /6 and then /7 block both have better internal webbing that make them stiffer for the larger engine capacity.

[Rob Frankham]

If you don't have a use for a /5 engine, I wouldn't bother. Although some parts are interchangeable (with varying degrees of engineering involved), very few are identical (Con rods and... errr... con rods is about all I think).

In addition, the fact that there is a jug with a stuck piston probably means that it isn't in the best condition to start with.

If he was giving it away, I might take it just in case but I wouldn't give money for it.

Regards

Rob